PATTERNS CONSPICUOUS IN NATURE. 



Text-figfiire 1. 



385 



V 



bK 



E B 



1 foot. 



Ground plan of apparatus used for measuring visibility of objects and blending 

 distance of patterns. A = when object and background are illuminated by tlie 

 same ligbt. B = when illuminated by ditferent light. 



c=standard candles, i' = screens, E=eye, B=background, o = object, 

 G=glass plate. 



Experiment No. 1. 



A. Candles 1 ft. apart :' conditions as in text-tig. 1 : candles distant 1 ft. from glass 



plate on which object was placed : background of grey paper 2 ft. from glass 

 plate. Object of black needle-paper, 36 sq. mm. The following ten readings 

 (in feet) of the greatest distance at which the object could be seen, were made at 

 intervals of five minutes :— 72, 72-8, 72-9, 72-8, 74-4, 73-4, 74-1, 73'5, 727, 72^9. 



B. Candles 1 ft. apart : patterns 2 ft. 1 in. from candles : pattern consists of 



alternate black and white squares, 25 sq. mm. : pattern covered. 16 sq. cm. 

 The following ten readings (in feet) of the distance at which the pnttern 

 blended into "an even a,-rey tone, were made at intervals of five minutes : — 

 31, 33, 33-6, 34-1, 34, 33-9, 34-5, 337, 33-8, 34-3, 34. 



following experiment (no. 2) was made as it has a bearing on 

 the relative visibility of patterns, as will appear later. It shows 



